1. Field of the Invention
The present invention relates to a random access memory (MRAM). More particularly, the present invention relates to a magnetic random access memory with vertical anisotropy ferrimagnetic structure, and a method of reducing the critical current of the MRAM.
2. Description of Related Art
Magnetic random access memory (MRAM) is a non-volatile memory technology to store digital data. The conventional MRAMs use horizontal anisotropy magnetoresistance elements or cells to store data.
Refer to FIG. 1. A MRAM 100 in accordance with the prior art comprises a biasing layer 110, a pinned layer 120, a spacer layer 130 and a free layer 140. The biasing layer 110 is an anti-ferromagnetic layer to pin or secure the pinned layer 120 magnetization in a given direction. The pinned layer 120 and the free layer 140 are both ferromagnetic. The spacer layer 130 is made of non-magnetic materials or insulating materials.
Refer to FIG. 2. The magnetization 141 of the free layer 140 is parallel to the magnetization 121 of the pinned layer 121, and both of them point towards the same direction. In this circumstance, magnetic resistance of the MRAM 100 is at a low state. However, if the direction of the magnetization 141 of the free layer 140 is reversed relative to the direction of the magnetization 121 of the free layer 120 as denoted by numeral 141′, in this circumstance, magnetic resistance of the MRAM 100 is at a high state.
Conventional method to change the directions of the magnetization 141,141′ of the free layer 140 uses two quadrature currents passing through the MRAM 100. Accessing is accomplished by measuring the resulting currents of the quadrature currents through the MRAM 100. Therefore, each cell of the MRAM 100 must be kept in a given volume. Otherwise, the accessing currents will influence other cells neighboring the cell matrix of the MRAM 100. The conventional method that changes the directions of the magnetizations restricts density of the cells matrix, hence increases power consumption.
The problems that aforementioned MRAM 100 faced are inevitable under conditions in which the present magnetoresistance elements have a multi-layer structure with various materials. Therefore, there is a need to provide an improved MRAM and a method of reducing critical current of the MRAM to mitigate or obviate the aforementioned problems.